Re: [ATM] Quick fractions question....

["vladimir sacek" <vla@toast.net>]

1/20 wave (p-v?) means nothing. It can be anything
from relatively small local surface error to a smoothly
distributed over the entire surface. Since what you
see is a zonal defect, all you can do is determine
approx best and worse case scenarios. The worst case
scenario is that the reference flat's surface deformation
nearly coincides with that of the mirror tested, with
the sign of deviation same for both (for instance, both
depressed). In that case, actual mirror error is additive,
0.125+0.05=0.175, or nearly 1/6 wave p-v. Best case
scenario is if the two zonal deviations nearly coincide
while having deviations of opposite sign, when the error
subtractive: 0.125-0.05=0.075 or ~1/13  wave.

For any other scenario, actual mirror surface error would
fall in between these two values.

Vlad


----- Original Message ----- 
From: "Thomas Janstrom" <thomas@moiler.com>
To: "'ATM'" <atm@atmlist.net>
Sent: Sunday, January 29, 2006 9:33 PM
Subject: [ATM] Quick fractions question....


Could some please clarify something for me? I have a 5" 1/20 wave
reference flat, I'm testing a 4" flat I'm making on it, now I see a
deviation of ¼ fringe, which would equate to a deviation of 1/8 wave,
right? So what is the "true" accuracy of this flat? Is it 1/8 of 1/20 or
what?



BTW the error is a slightly depressed zone about ¾" in from the edge
going inwards about ¾" or so, it fades out to a relatively "flat"
central zone.



Cheers, Thomas

HYPERLINK "http://www.tjanstrom.com/"www.tjanstrom.com

HYPERLINK "http://www.norsewines.com.au"www.norsewines.com.au




-- 
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.375 / Virus Database: 267.14.23/243 - Release Date:
27/01/2006

_______________________________________________
ATM mailing list http://www.atmlist.net/ 

_______________________________________________
ATM mailing list http://www.atmlist.net/